Anorexia nervosa (AN) is a severe illness associated with substantial morbidity and a mortality rate of 10% per decade of illness, with half of these deaths resulting from suicide. While treatment programs report modest success at medical stabilization and weight gain at the end of such programs, patients with AN frequently exhibit symptoms of depression and anxiety, and relapse rates are extremely high. This study aims to expand our understanding of serotonergic activity in these challenging patients by carrying out several studies and assessments. First, the serotonin precursor trytophan (TRP) and the ratio of TRP to large neutral amino acids (TRP/LNAA) in the blood, will be measured in patients with AN admitted to an inpatient treatment program, at time of the admission, after medical stabilization, and upon normalization of weight. Second, the study will measure the concentration of the serotonin metabolite 5-hydroxyindoleacetic acid in the cerebrospinal fluid (CSF 5-HIAA) upon weight restoration and compare these results to available information from a historical control group in an attempt to replicate a published finding that patients with AN may develop a super-normal level of brain serotonin when they are re-fed. The study will also correlate the level of CSF 5-HIAA with levels of TRP/LNAA. Third, patients will undergo acute tryptophan depletion and sham TRP depletion, with standardized assessments of mood and eating attitudes and behaviors before and after this intervention.